DE3040992A1 - ALUMINUM OXIDE GRINDING GRAIN AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Description

THE CARBORUNDUM COMPANY
Niagara Falls, New York
(United States of America)

* ■ Aluminum oxide abrasive grain

and
Process for its manufacture

Abrasive grain based on essentially pure aluminum oxide with 0.25 to 6% additives or residual impurities from the starting material has proven to be one of the most versatile and technically most important abrasives. Abrasive grain of this type is found in many different Grinding work on common metals application.

Although the proportion of impurities is very low, they can significantly reduce the grinding performance of the abrasive grain influence. By changing the level of impurities and the rate of cooling and solidification of material melts, various types of aluminum oxide abrasive grain have been developed over the years. The individual types differ in a different combination of properties, such as hardness, Toughness, frictional properties, microstructure, fracture properties, thermal behavior, etc., making each Type for specific grinding work using abrasives on backing or bonded abrasives was particularly suitable.

130 02-2 / & 712

So far no competitive material could be available the better the sanding properties than essentially pure aluminum oxide, especially when grinding with light to moderate pressure.

Try aluminum oxide with other oxides in higher concentrations than before to alloy were undertaken. Zirconium dioxide proved to be a particularly promising material. Attempts in which aluminum oxide with at least 10% by weight of zirconium dioxide brought a certain success melted and the melt was rapidly solidified.

In US Pat. No. 3,156,545, it is described that an abrasive grain with a removal rate which corresponds to that of the Alumina is comparable, can be produced by rapid cooling of a melt that contains 15 to 60% by volume Contains glass, such as silica, which forms a vitreous matrix in which zirconia and alumina particles are embedded. However, the removal rate of the abrasive grain is not significantly better than that of steel of alumina.

Other US and UK patents use alumina / zirconia abrasives described that perform better than aluminum oxide in special fields of application demonstrate.

For example, US Pat. No. 3,181,939 describes a high-strength abrasive grain which is produced by melting α-aluminum oxide and 10 to 60% by weight of zirconia and rapid cooling of the melt can be obtained. The abrasive grain is particularly suitable for cleaning steel (i.e. grinding work with high pressure), with a high strength is required. However, the patent states that the et-alumina is of high purity - in the

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Usually at least 99.8 wt.% Al ₂ O ₃ - must be and that the zirconium dioxide should also have a purity of at least 99%.

According to U.S. Patents 3,891,408 and 3,893,826, the best grinding and polishing properties are obtained when the ratio of the zirconium dioxide to the aluminum oxide is chosen so that a eutectic structure arises when the aluminum oxide / zirconium dioxide melt is rapidly cooled.

< US Pat. No. 3,891,408 discloses the very rapid crystallization of eutectic or almost eutectic melts of aluminum oxide and zirconium dioxide. It is believed that the optimum eutectic composition and moderate pressure performance is 43% by weight zirconia; in any case, however, the proportion of zirconium dioxide in the abrasive grain is 35 to 50% by weight. The zirconium dioxide in the material is in the form of rods (or platelets) which on average have a diameter of less than 0.3 μm, and at least 25% by weight of the zirconium dioxide is in the tetragonal crystal form. The solidified melt consists of cells or colonies with a width of 40 μm or less. groups

v. of cells with identical orientation of the microstructure

form granules that typically contain 2 to 100 or more cells or colonies. When shredding the material the break occurs at the grain and cell boundaries. The abrasive grain produced in this way should have a very high strength in connection with very desirable micro-fracture properties.

The abrasive grain produced according to US Pat. No. 3,891,408 is characterized by an almost eutectic composition due to its unusual usefulness for sanding work with light pressure. When used as an abrasive

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On the backing for grinding work with little or moderate pressure, there were improvements of over 100% compared to this standardized comparative abrasives of known type. When used in bonded abrasives, also achieved significant improvements when sanding with little or moderate pressure.

The properties of the abrasive grain according to U.S. Patent No. 3,891,408 are in contrast to those of abrasive grain with a lower zirconia content, for example 25% of ZrO _2, which is very hard and grinding with a high arrival r pressure, such as for cleaning of steel , is used.

The task now was to create a highly effective aluminum oxide / zirconium dioxide abrasive grain to be made available for grinding work with low or moderate pressure, its grinding performance equal to or better than that of the eutectic or almost eutectic abrasive grain Composition according to US Pat. No. 3,891,408, but which contains less zirconium dioxide. Furthermore was a To specify the method of manufacturing this abrasive grain.

According to the invention, this object is achieved by the claims 1 and 10 are resolved. Advantageous further developments of the invention are set out in the subclaims 2 to 9 as well as 11 and 12 indicated about the Claim 12 provides information on the use of the abrasive grain.

As can be seen from claim 1, there is a reduction the zirconium dioxide content in the abrasive grain thereby possible that "the abrasive grain titanium dioxide or a reduced form thereof in an amount of 1 to 10 wt .-?;, expressed as oxide, added and the proportion of impurities to a maximum of 3% by weight, expressed as oxides, limited '. The specification of abrasive grain components as oxides is a common practice in ceramic

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technology, but does not mean that the titanium or the impurities also exist as oxides. In fact, this cannot be the case, as can be seen from the description below emerges. Since, however, in the usual analysis methods for abrasives, the components as Oxides are determined and specified, this practice has been adopted here. With the usual analysis methods the constituents, with the exception of aluminum oxide, are determined and reported as oxides; the rest is called alumina specified. The analytical values for abrasive grain are also expressed here on this basis.

In the following description, all details are given about the amounts of titanium dioxide or a reduced form thereof or the impurities in the abrasive grain analytical values expressed as oxides.

The amount of titanium dioxide or a reduced form thereof (for example a suboxide, oxycarbide or carbide) in the abrasive grain is 1 to 10% by weight, most preferably 1 to 5% by weight. Although it has been found that such high proportions of titanium dioxide or a reduced form thereof have an adverse effect on the performance of abrasive grain with a nearly eutectic ^ Al ₂ O ₃ VZrO ₂ ν composition in common grinding work,

it has been found that, in the case of an abrasive grain containing 27 to 35% by weight of ZrO ₂ , they surprisingly improve the grinding performance when grinding with low to moderate pressure. The mechanism underlying this surprising improvement in the properties of the abrasive grain by the titanium dioxide or a reduced form of the same is not known; it could consist in an increase in the coefficient of friction and the heating rate when the abrasive grain comes into frictional contact with the metal, the faster heating supporting the penetration of the abrasive grain into the metal.

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If there are impurities in the abrasive grain, it is either residual impurities from the starting materials or intentionally added additives. Such additives can be added, for example, to promote refining. For example, iron and coal are added to bauxite melts in order to reduce the iron oxide and silicon dioxide content and keep it within limits. It is common, in fact, add the lugs increases to a certain final analysis or to set undesirable phases to bind and to facilitate their separation by precipitation onto the hearth of the furnace or r by evaporation on the surface of the melt.

Since it is not economically justifiable to completely remove all impurities, the abrasive grain can be certain Contain impurities that can affect and reduce its performance. It is essential that the Content of such substances is kept within certain limits. Such substances are alkalis (soda, potash, Lithium carbonate), alkaline earths, silicon dioxide and iron oxides. They can be used individually, together or in conjunction with the main phases or in reduced forms, such as Carbides, nitrides and even free metals.

The potency of the harmful impurities varies. Alkalis, especially soda, have one special feature harmful effect on performance. Silica is at the zirconia levels of that described herein Abrasive grit is also harmful, but to a lesser extent as alkalis. The presence of alkaline earths in the end product is easier to avoid, but is also or slightly less harmful than the presence of silica. Note that with higher zirconium dioxide contents, than they are used here, for example in the case of a eutectic aluminum oxide / zirconium dioxide mixture, silicon

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dioxide can be an advantageous constituent, as described, for example, in German patent application P 29 007.5.

The content of impurity phases in the finished product should therefore be kept at an economically justifiable minimum amount. These are determined by the choice, costs, availability and quality of the raw materials used, aluminum oxide and zirconium dioxide, as well as the extent to which they can be modified economically by the melting technology used. Regardless of the starting raw materials and the melting process used, the end product may contain a _{maximum of 0.1% Na 2} O and a maximum of 1.5% SiO ₂ , better still a maximum of 1% SiO _2. With these upper limits of Na ₂ O and SiO ₂ , their harmful influence is not too great and can be partially neutralized by adjusting the titanium dioxide content. In addition, the total content of MgO, CaO and Fe ₂ O _{3 must} not exceed 1.5%.

The abrasive grain can be made by rapidly solidifying a melt of aluminum oxide and zirconium dioxide, which is still the required amount of titanium dioxide or a reduced form thereof and possibly contains impurities will. Rapid solidification is brought about by bringing the melt together with a heat-dissipating material and must be within a period of 3 minutes, better within a period of less than 1 minute and ideally take place within a period of less than 20 seconds. The heat dissipating material or cooling medium can consist of metal balls, metal rods or metal plates or also from chunks of previously melted There are abrasive grain on which the melt is poured.

An important criterion of the cooling medium is that it has such a shape, size and mass that it contains hollow

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Forms spaces into which the melt can penetrate. The coolant must therefore offer the melt as large a surface as possible so that solidification is achieved within the prescribed period of 3 minutes or, better, less than 1 minute. The cooling medium must be able to absorb the heat energy of the melt at a high heat transfer rate, without melting and without deteriorating its properties, so that it can be used repeatedly. An example of such a cooling medium is that described in British Patent Application 41763/77, "rod mold ^11. Other known r * .. cooling means may also be used.

Another advantageous cooling method is that the melt is not poured onto the cooling medium, but this is entered into the melt and removed again when a layer of product is deposited on it Has.

After separation from the cooling medium, the solidified mass can be used to produce an abrasive in a known manner Way to be crushed. The crushing process can consist of a coarse crushing in a primary jaw crusher, Further shredding in a secondary roller crusher and finally fine shredding in a canal

ry mill or hammer mill. To different abrasive grit To maintain shape, the grinding process can be modified. This is a well-known method to expand the application range of an abrasive grain of a certain composition. For example, for certain An easily breakable, soft, elongated, sharp-edged grit required for abrasives on a backing while certain bonded abrasives have a sharp-edged, but more "block-shaped", hard abrasive grain can be cheaper.

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The grain size of the abrasive grain produced can be between 6 and 1000 according to the standards issued in 1971/72 the FEPA or the U.S. Department of Commerce Commercial Standard CS271-65, issued April 12, 1965, move. A grain size between 6 and about 180 is advantageous, preferably between 14 and 80.

The abrasive grain can be used for the production of coated abrasives or for the production of bonded abrasives can be used in a conventional manner. The abrasive grain can be the only abrasive in these products or used in conjunction with known abrasives.

Using an example, the production of the abrasive grain is explained in more detail below.

The aluminum oxide required for the abrasive grain to be produced can be in the form of bauxite or calcined alumina, obtained by the Bayer process, or as excess abrasive grain, containing a substantial amount of alumina. The one in the abrasives industry In addition to aluminum oxide, the bauxite used generally also contains 3 to 4.5% by weight of titanium dioxide, 3 to V 8% by weight silicon dioxide and 3 to 10% by weight iron oxide

(Fe ₂ O ₃ ).

The bauxite can be synthetic bauxite, unpurified calcined bauxite or partially purified bauxite (aluminum oxide, produced by melting and reducing calcined bauxite with metallic iron and coal). If more uncleaned If calcined bauxite is used directly, iron and carbon must be added to the bauxite-zirconium dioxide mixture, to remove as much iron oxide and silicon dioxide as possible. The titanium dioxide content can also be used can be reduced to too low a value, so that a

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Addition of titanium dioxide to adjust the final composition may be necessary.

Synthetic bauxite is made by combining or mixing pure alumina with desired impurities such as Titanium dioxide, made and used in place of natural bauxite.

Pure alumina can be excess high alumina abrasive grain or alumina obtained by the Bayer process. The latter is available in two forms in r trade, which differ in their sodium content:

low sodium calcined clay containing 0.1 wt% or less Na ₂ O; and normal calcined clay containing 0.5 to 0.3 wt% Na ₂ O.

Baddeleyite is best used as zirconium dioxide in the manufacture of the abrasive grain, which is usually the case

95 to 99% by weight of zirconium dioxide, 0.3 to 3% by weight of silicon dioxide, 0.5 to 2% by weight of titanium dioxide and 0.5 to 2 wt% iron oxide

contains ν. A content of hafnium oxide HfO ₂ is included in the content data for zirconium dioxide.

Compared to bauxite, baddeleyite contains smaller amounts of silicon dioxide, titanium dioxide and iron oxide than unpurified Bauxite.

Zirconia bubbles can also be used as zirconia be used when melting zirconia or purified Zirconia can be obtained.

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The titanium dioxide required to melt the abrasive grain, unless it is in the other starting materials is contained, can be added in the form of commercially available rutile, the at least 90%, better over 95% titanium dioxide contains.

The required proportions of the main raw materials are usually premixed with the necessary addition of carbon, usually in the form of petroleum coke or graphite, and iron. The necessary amounts of carbon and iron, if the latter is required, - can easily be calculated by a person skilled in the art on the basis of the analysis of the starting materials. If the titanium dioxide content falls below the required value during melting, the amount of titanium dioxide required _{to restore the necessary TiO 2 content can be added.}

In a preferred embodiment, the residual impurities are of the end product regardless of the raw materials used and the melting technique used below the following limits:

Silicon dioxide <1.0% by weight, best <0.5% by weight. Total content of alkalis (Na ₂ O) and alkaline earths (CaO and MgO) <1.0% by weight, best <0.5% by weight, of which Na ₂ O <0.1% by weight.

The melting of the pre-mixed raw materials is usually carried out in a carbon electrode arc furnace at temperatures of typically more than 1800 ⁰ C.

After melting, refining and - if necessary - restoring the TiO ₂ content, the melt is poured into or onto a suitable cooling medium, in or on which the solidification preferably occurs within one minute or better within 20 seconds after contact with the cooling medium takes place.

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It is assumed / that any cooling method or any cooling medium is used which has a high thermal conductivity, for example of more than 21 kW / m- ° C (18 kcal / mh ° C) at 1200 ⁰ C, and in which the greatest layer thickness of the cast material is preferably at most 2, most preferably at most about 0.5 cm.

Coolant, the lower thermal conductivities have as fragments of previously solidified melts, can · be used, the layer thickness of the cast melt is provided correspondingly lower, in the case of chunks previously ER- f starrter melt, for example less than 0.7, and most preferably

less than 0.3 cm.

Suitable coolants not only have to have high thermal conductivity, but also have high melting points. For these reasons and because of its relatively low Cost and abundant availability, steel is a good coolant. Another example of an economical one useful coolant is cast iron. Examples of other good coolants are chromium, nickel, zirconium and theirs Alloys, but they can be too expensive for technical purposes.

ν After solidification, the mass obtained becomes the desired one Crushed grain size and shape. The crushing is done by breaking in the jaw crusher, further crushing in impact or roller crusher and fine grinding in impact mills, i.e. with the help of well-known industrial ones Comminution process, achieved.

As has been found, the zirconium dioxide in the abrasive grain obtained is generally 10 to 40% tetragonal Crystal form. In general, the content is in the tetragonal crystal form of zirconia the lower the higher the residual content of the abrasive grain

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on silica.

Overall, there is the microstructure of the abrasive grain obtained from two parts:

1. primary alumina crystals found in

2. a eutectic matrix made of aluminum oxide and zirconium dioxide are embedded.

The volume fraction of the primary aluminum oxide crystals is approximately ζ 40% with a zirconium dioxide content of 34% by weight and approximately with a zirconium dioxide content of 27% by weight

52%.

With the optimal eutectic abrasive grit mass according to US Pat. No. 3,891,408, little or no primary aluminum oxide crystals are present; theoretically there shouldn't be any. At the upper limit of the zirconium dioxide content according to this patent specification - at 50% by weight ZrO ₂ - the abrasive grain contains primary zirconium dioxide crystals. The preferred embodiment of the subject matter of US Pat consists entirely of eutectic cells or colonies as much as possible.
C.

The microstructure of the abrasive grain according to the invention is different in this important respect in that it desirably contains 40 to 52 volume percent primary alumina crystals and must also contain 1 to 10% by weight of titanium dioxide or a reduced form thereof.

The primary alumina crystals in the abrasive grain according to the invention have a size of 5 to 50 μm and are predominantly smaller than 30 μπι. Often times they show one oriented structure of dendritic type in which the dendrites or groups of dendrites through the eutectic Ground mass are separated.

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The zirconia comes in the matrix in the form of Before rods or platelets, which are distributed in a basic phase rich in aluminum oxide. The diameter of the Rods or the thickness of the platelets should be 0.02 to 0.4 μm. The typical distance between the chopsticks is on average less than 0.3 μπι, but come There are also smaller distances that can often no longer be clearly resolved under the scanning electron microscope.

The basic mass consists of groups of zirconium dioxide rods or plates with a high degree of orientation, / "creating the matrix between the primary alumina crystals divided into a series of eutectic colonies or areas. The size of the colonies or areas typically moves between 5 and 30 μπι.

The crucial phase of titanium dioxide or a its reduced form is likely to exist as a solid solution with the primary aluminum oxide crystals, but it is assumed that that most of it is at the interface between the primary alumina crystals and the eutectic Basic mass, especially at the interface between the eutectic colonies or areas that the eutectic Form a matrix in which the primary aluminum

ν oxide crystals are embedded. The residual impurities

are also likely to be in these two places, where they are used individually or in conjunction with others or the Main phase including the titanium dioxide occur.

The invention is explained in more detail by means of examples. The following melting and cooling procedure was used in these examples applied.

The melting was done in a 100 kV AC furnace made two graphite electrodes 76 mm in diameter, the distance between which changed between 10 and 25 cm and whose

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Height could also be adjusted. A premixed approach from the composition under investigation was placed in the furnace and the arc started by inserting a graphite bar between the electrodes at a Ignited from a distance of 10 cm.

After a starting bath of molten material was obtained, additional portions of the mixture were added in portions added, and the height and the distance of the electrodes were adjusted so that at a voltage from 65 to 90 V a current of 600 to 1000 A flowed.

In this way, the melt was treated in the furnace for 30 to 40 minutes; then a first cast was made. The electrodes were pulled up over the surface of the melt, and after waiting about 2 minutes the melt was converted into a shape containing steel balls 25 mm in diameter or into a rod shape according to of British patent application 41763/77 cast with steel rods 25 mm in diameter and 5 mm apart.

The amount of material produced in each cast ranged from 9 to 18 kg, and for each particular composition a number of casts were made.

The solidified material produced by the method described above was used to produce abrasive grain crushed. Typically, the material was first in a jaw crusher to a grain size of about 8 grain and finer and this product then in a secondary roll crusher to a grain size of 16 Refined grain and smaller. This material formed a stock product. After a rough magnetic separation to the Removing free iron from the crushers, the stock product was carefully cross-balanced Grain sizes for the manufacture of products

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and sieved for physical and chemical analysis. Here, abrasive grains of grain sizes 16 to 80 were used Grain received; these are the most common grain sizes for carrying out grinding tests. For commercial Purposes, a complete range of grain sizes could be produced.

EXAMPLE 1

A series of melts were prepared using the procedure described above. The starting materials and the composition of the mixtures are given in Table 1,

Table 1

Approaches with Al ₂ O ₃ from approaches with low synthetic Na ₂ O content table bauxite starting materials (wt .-%) (wt .-%)

F357 F358 F359 F36O F361 F362 F363 F364

Calcined clay
with low Na ₂ O content (+ 99% Al ₂ O ₃ ) 65.5 63.0 69.5 67.0 64.7 62.2 68.65 66.18

Baddeleyit

(98% ZrO ₂ ) 32 32 28 28 32 32 28 28

Rutile (95% TiO ₂ ) 2.5 5.0 2.5 .5.0 2.5 5.0 2.5 5.0

e silicon dioxide

(98% SiO ₂ ) - - - 0.6 0.58 0.64 0.62

Iron oxide

(87% Fe ₂ O ₃ ) - - - 0.2 0.19 0.21 0.20

100 100 100 100 100 99.7 100 100 Addition of fine graphite 1.0 1.2 1.0 1.2 1.0 1.2 1.0 1.2

Note: The graphite additions appear to be excessive. That

is not the case, however, as a large part of the graphite is oxidized in the crust and does not get into the melt. The amounts given were determined empirically and produced good results. When using coarser carbon, the amount can be reduced considerably.

The melts of the batches according to Table 1 were poured into a 25 mm rod mold of the type described above and after solidification, comminuted in the manner described above. The abrasive grit had the one in the table given analysis.

Table 2 Al, 0, TiO, %-Salary Fe ₉ O, SiO, Well, 0 65.96 1.82 CaO 0.15 0.5 0.03 Melt no. ZrO, 65.07 3.35 0.04 0.05 0.3 0.02 F357 31.5 65.22 1.82 0.01 0.01 0.3 0.04 F358 31.2 65.15 3.26 0.01 0.01 0.5 0.04 F359 28.6 65.55 1.67 0.04 0.04 0.8 0.03 F360 29.0 63.73 3.28 0.01 0.01 0.9 0.03 F361 31.9 68.40 1.73 0.04 0.02 0.7 0.03 F362 32.0 66.77 3.26 0.02 0.02 0.9 0.02 F363 29.1 0.03 F364 29.0

EXAMPLE 2

Exactly balanced abrasive grain size 36 of the im

C Example 1 specified compositions were used for grinding

tapes processed. A sample of conventional, brown, fused G52E grade alumina that is is widely used for the production of abrasive belts, was also made into abrasive belts. the Grain size of sample G52E was exactly crossed and matched to test samples F357 and F364.

About the influence of dust on the abrasive grain and possible differences in the electrostatic application properties All abrasive grain products have been washed and surface treated to remove to ensure a standard conductivity on the surface.

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The abrasive grain pretreated in this way was then electrostatic with a DC voltage of 19 kV within a Time span of about 20 seconds over a distance of about 25 now sprayed onto a flexible surface.

The flexible base consisted of a polyester fabric with a 4/1 satin weave and about 41 χ 16 threads / cm ² , which was previously coated with an adhesive mixture of a commercial one-stage liquid phenolic resin with a phenol / malaldehyde ratio of about 1: 1.6 had been. The adhesive also contained ground limestone f- with a particle size of about 17 to 25 μm. The ratio of phenolic resin adhesive to limestone was 58 to 42% by weight. The adhesive also contained 0.1% by weight of a wetting agent (MANOXOL OT). The adhesive had a viscosity of about 0.8 Pa-s at coating temperature. For abrasive grain of grain size 36, a coating of 0.28 kg / m ^{2 was} used.

The fabric with the abrasive grain applied in a concentration of about 0.9 kg / m ² was carefully dried ^{at 75 °} C. for (at least) 1 hour ^{and then at 90 °} C. for at least 3 hours.

A top coat was then applied to the grain surface in order to partially fill the gaps between the abrasive grains and to improve adhesion and bonding. The top coat was about 0.65 kg / m ² . The composition of the top layer material was the same as that of the adhesive, but the top layer material still contained 1.5% by weight of PYROGENE, which prevents the top layer from "sagging" during the final drying and curing process.

A typical curing process consisted of a heating of at least 1 hour at 75 ⁰ C, at least 3 hours at 90 ⁰ C, at least 1 hour at 100 ⁰ C and minde-

13 0 0 2 2 ² / o 7 1 2

at least 12 to 14 hours at 107 ⁰ C.

After curing, the product was left in a humid atmosphere of + 95% relative humidity for at least 24 hours kept. Thereafter, the product was bent in three directions by 45 ° in order to facilitate handling in the manufacture of Sanding belts to facilitate. Using known methods, the coated material was turned into abrasive belts in size 208 cm χ 5 cm.

In this way, abrasive belts were made with the experimental abrasive grain types F357 to F364 according to Table 2 and the abrasive grain made from conventional fused alumina manufactured.

The abrasive belts thus obtained were then used on a known high-performance abrasive belt testing machine of mild steel workpieces in the form of rolled angle profiles with a cross section of 19 mm χ 19 mm χ 3.2 mm and a length of about 1220 mm. In this test, the tape was worn in a conventional manner placed the back frame and arranged the workpiece so that its cross-section is just below the horizontal diameter of the pressure roller touched the tape.

The sanding belt was driven at a speed of 1372 m / min and a pressure roller of 356 mm diameter guided. A feed force of 7.26 kg dead weight was exerted on the workpiece, and a The grinding process consisted of 50 contacts of 2.25 seconds each with an interval of 10 seconds between every contact. The amount of metal removed (i.e. abraded) was measured after each grinding process, and the experiment was continued until the amount of metal removed in one grinding operation was less than 66 g. The total weight of the

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The metal carried and the total weight loss of the belt gave the relative abrasive performance of the belt.

The abrasive belts made from the various abrasive grains showed those listed in Table 3 Grinding services.

Tabel Weight
loss
d. Band
(G) 3 2nd series of tests Weight
loss
d. Band
(G) 1st series of tests 12th Abgetra
genes
metal
(G) 9.0 Abrasive grain Abgetra
genes
metal
(G) 10 1292 10.0 F357 1888 11 1189 10.0 F358 1265 13th 1279 checked- F359 1470 12th - not 10.0 F360 1848 19th 1154 11.5 F361 1408 12th 1361 11.0 F362 1768 checked- 1119 12.0 F363 1462 9 1267 8th F364 -not 415 G52E (manu-
Coming. Al ₂ O ₃ ) 571

The high grinding performance of the abrasives according to the invention versus conventional fused alumina. Improvements of 100 to 230% were obtained. The difference between the two test series is the contact time. Everyone passed the first series of tests Grinding process from 50 contacts, each 2.25 s duration; in the second series of tests, the contact time was for the 50 Contacts 2 s.

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EXAMPLE 3

The test values for abrasive belts are based on a procedure what is referred to in the industry as low frequency loops, i. the number of times per second that each cutting point touches the workpiece is proportional low. The cutting frequency for tapes depends on the ratio of the raised surface parts to the grooves of the Pressure roller and is typically 1 to 10 s. To take advantage of the new abrasives at high cutting frequencies To check, tests have also been carried out in which the abrasive grain is bonded to grinding wheels 178 mm diameter was incorporated. With these, the cutting frequency per grain can be up to 100 s.

Essentially the same procedure was used as described in Example 2, except that the Abrasive grain was applied to a backing made of high-strength fiber.

The binder for the panes was a one-stage liquid phenolic resin with a phenol / formaldehyde ratio of 1: 1.55. 15% by weight of ethanediol and ground limestone in a ratio of parts by weight of calcium carbonate powder to 11 parts by weight of phenolic resin were added to this phenolic resin. A wetting agent (MANOXOL OT) and enough water were also added to the binder so that the viscosity of the binder was 1.7 Pa · s. The binder was applied with a layer thickness of 0.35 kg / m ² . The abrasive grain layer electrostatically sprayed onto the binder layer had a layer thickness of 1.4 kg / m ² (Note: Depending on the specific weight of the abrasive grain, the application weight was modified so that a constant volume was obtained.)

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The application voltage was 19 kV DC over a 25 mm gap and the application time 20 seconds.

The coated product was then dried ^{at 90 ° C. for at least 3 hours.}

Then a top layer made of the following components was applied:

35% by weight of a one-stage commercial liquid phenolic resin having a phenol / formaldehyde ratio of - 1: 1.6, 65% by weight cryolite filler, 2.5% by weight iron

* - oxide pigment and 0.1% of a wetting agent (MANOXOL OT). the

Top layer was applied in an amount of 0.69 kg / m ^a .

The product was at least 4 hours at 90 ⁰ C and 14

dried and cured ^{at 107 °} C. for up to 16 hours and

then in a humid atmosphere for 24 hours

+ 95% relative humidity stored. It was then bent over a ball in the usual manner.

Discs with a diameter of 178 mm were punched out of the abrasive in a known manner.

To make the grinding wheels, they were exactly crossed Matched abrasive grain of grain size 36 of the abrasive grain products listed in Table 1 as well as the conventional one fused alumina product from Example 2 was used.

The grinding wheels were made on a pressure wheel attached to an aluminum alloy, which was provided with a 1.5 to 3.2 mm thick rubber pad. The disc was arranged so that it was the end of a mild steel pipe of 203 mm diameter, 6.4 mm wall thickness and approx

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254 mm initial length touched. The workpiece was in the vertical plane by 2 to 3 ° from the horizontal and inclined in the horizontal plane by 1 to 2 ° relative to the normal. The workpiece rotated at a peripheral speed of 21.3 m / min and the disc with a peripheral speed of 3048 m / min. The disc was pressed against the workpiece with a dead load force of 22.7 kg.

The workpiece was during a contact time of. 15 seconds ground with the disk, then removed, weighed overall _f, cooled with water and dried. The grinding

The process was repeated according to this pattern until the amount of metal removed in the contact time of 15 seconds was less than 20 g. The amount of metal removed up to then and the total weight loss of the disc were chosen as a measure of the abrasive performance. In this way, the abrasive grain products became F357 to F364 as well as the standard aluminum oxide G52E. The results are shown in Table 4.

Table 4

Abrasive grain Metal removal
(G) Weight loss
the disc
(G) F357 ~ | 1004 2.73 F358 i Al ₂ O ₃ with low 918 2.88 F359 j Na ₂ 0 content 1071 2.80 F360 J 1171 4.05 F361 Ί 637 1.93 Γ Synthetic bauxite
F363 j 735
660 2.68
2.17 F364 J 810 2.60 G52E (standard Al., O ₃ ) 537 2.20

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EXAMPLE 4

In order to compare the performance of the abrasive grain according to the invention in bonded abrasives, after Process described above, two further melts from the batch mixtures listed in Table 5 below manufactured.

Gemi s ch-group f Al ₂ O ₃ with low
I according to Na ₂ O content
J rutile
I silicon dioxide Heat no. F366 _ Table 5 V »iron (III) oxide F365
(Wt%) 64.2
5.0
0.6 Mixtures of
synthetic
bauxite '66.7
2.5
0.6 0.2 0.2 30jO Baddeleyit 100.0 100.0 1.2 Fine graphite 1.0

The analysis of the finished abrasive grain products is shown in Table 6.

Al ₂ O ₃ ZrO ₂ TiO ₂ CaO

Fe ₂ O ₃ SiO ₂ Na ₂ O

Table 6 F365
(Wt%) F366
(Wt%) 68.72 65.25 28.60 30.20 1.76 3.24 0.04 0.02 0.14 0.24 0.76 1.08 <0.10 <0.10 0.29 0.35 (2 h, 1300 ⁰ C)

Specific weight 4.42 g / cm ³ 4.47 g / cm ³

13 0 0 2 22J * 0-7 1 2

The abrasive grit products were made to have the same grit shape Grain size distribution with a conventional brown aluminum oxide abrasive grain obtained by melting bauxite was manufactured and is widely used in bonded abrasives under the name EDR, carefully crossed matched.

Grinding wheel approaches

The following was used to make the test grinding wheels Abrasive grit used:

64% -0.70 to +0.59 mm

36% -0.59 to +0.50 mm

The approaches to making bonded abrasives were:

EDR F365 F366 (Wt%) (Wt%) (Wt%) Abrasive grain 76.02 78.02 78.20 Binder Mix 22 17.10 15.68 15.54 CS 303 1.71 1.57 1.55 CL 50 5.17 4.74 4.70

Note: The different percentages resulted from adjustments due to the different specific weight of the abrasive grain products F365 and F366 compared to the abrasive grain EDR (γ = 3.95 g / cm ³ ). This ensured that the volume of the abrasive grain to the binder phase remained constant.

The binder mixture 22 consisted of a finely powdered mixture of 36.9% by weight of a powdered novolak with a phenol / formaldehyde ratio of 1: 0.71 and 63.1% of a mixture of whiting and potassium aluminum fluoride.

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3040392

CS 303 is a powdered novolak with a phenol / formaldehyde ratio from 1: 0.95. CL 50 is a one-stage liquid resole with a phenol / formaldehyde ratio from 1: 1.2.

The approaches were made by first mixing the abrasive grain with the liquid Resole CL 50 and the binder mixture 22 was mixed to build up a binder layer on the wetted grain. Then the powdered Novolak CS 303 was added and mixed with the other ingredients to form a free-flowing mixture that was ready to be molded.

Grinding wheels

The blends described above were used to make grinding wheels with a recessed center portion of 178 mm in diameter and 6.4 mm thick, reinforced with fiberglass in the middle and an outer one Had reinforcement made of glass fiber fabric. The discs were made in a known manner and had after the following densities after pressing:

EDR F365 F366 (g / cm ³ ) (g / cm ³ ) (g / cm ³ )

Hard quality 2.41 2.63 2.65

Soft quality 2.32 2.54 2.56

Note: the differences in the densities resulted again from the different specific weights of the abrasive grain products, i.e. the volume of the abrasive grain compared to the binder is the same for every quality.

The grinding wheels were clamped together in stacks using metallic spacers and in this Hardened state. The hardening process consisted of about

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27stündigem heating to 179 ⁰ C and further lOstündigem heating to 179 ° C. The cured disks were dressed precisely to a diameter of 178 mm and checked for their density in the cured state before testing.

The discs were tested on a machine specially designed for testing such products. The disk was mounted on a shaft which rotated the disk at a speed of 6000 rpm. A mild steel workpiece in the form of a plate with the / ■. Dimensions 203 mm 102 mm 6.4 mm was taken under the

Disk attached so that the disk moved back and forth along the 102 mm 6.4 mm edge. The test disc was pressed against the workpiece with a dead load force of 5.9 kg at an angle equal to the Freehand grinding is common. The workpiece was set in a reciprocating motion, which is the pivoting motion simulated when grinding with a hand grinder. With this back and forth movement, the workpiece was with passed under the grinding wheel at a speed of about 9 m / min.

The test consisted of determining the amount of metal removed and the weight loss of the disc in one

Duration of contact between disc and metal of 2 minutes. The test was continued until the amount of metal removed in the contact time was less than 2 minutes than 30 g. The data obtained give the relative grinding performance of the tested abrasive grain in the form of average metal removal rate, grinding ratio and quality factor. The grinding ratio is calculated from the total amount of metal removed, divided by the corresponding weight loss of the disc. To avoid differences in the density of the grinding wheels by differences in the specific weight of the

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To compensate for the abrasive grain, all weight losses were lost of the wheels normalized to the volume that the standard aluminum oxide grinding wheels was equivalent (equivalent weight loss).

Those with the abrasive grain products F365 and F366 as well as dem Results obtained using standard EDR alumina abrasive grain are shown in Table 7.

Table 7 Medium
Metal-
abrasive
speed
age
(g / min) Grinding
behaves
nis Quality
factor* Abrasive grain Discs
quality 24.97 13.64 341 EDR
(Standard Al ₂ O ₃ ) soft 24.66 13.05 322 hard 27.87 16.74 467 F365 soft 27.64 20.64 571 hard 27.65 20.07 555 F366 soft 27.38 27.10 742 hard

* The quality factor is the product of the average metal removal rate and grinding ratio.

The data clearly shows the superior grinding performance of the abrasive grain products of the invention over fused Alumina in bonded abrasives. They also show the improvement brought about by the increase the titanium dioxide content of 1.76% for the product F365 to 3.24% for the product F366 is achieved. With the product F366 became an expressed by the quality factor Achieved a grinding performance that is 130% better than that of the standard aluminum oxide abrasive grain.

The above examples demonstrated the superior grinding performance of the abrasive grain products of the invention

130022 ^3/0712

familiarization with coated abrasives and bonded abrasives for low-level sanding work or moderate pressure against similar abrasives with molten aluminum oxide as the abrasive grain different conditions. The abrasives according to the invention gave improvements of up to 230% in products on a backing and of over 100% for bound products.

To give an idea of the grinding performance of eutectic alumina / zirconia abrasives, containing 40 to 43% by weight of zirconia and prepared in accordance with the main claims of US Pat. No. 3,891,408 was the grinding performance of a commercially available alumina / zirconia eutectic abrasive grain compared to that of molten alumina.

EXAMPLE 5

A commercially available eutectic Al ₂ O ₃ / ZrO ₂ abrasive grain was cross-matched with regard to grain size and grain shape, processed into grinding belt according to the method specified in example 2 and this was tested according to the method of example 4. The results shown in Table 8 were obtained.

Abrasive grain

Commercial eutectic abrasive grain
(40-43% ZrO ₂ )

Standard aluminum oxide G52E

Table 8

1st series of tests

Band-to-metal weight loss (g) (g)

1699

571

2nd series of tests

Band-to-metal weight loss (g) (g)

1236

415

10

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3040S92

The grinding performance of the eutectic abrasive grain was up 200% better than that of conventional fused alumina.

Note: In the 1st series of tests, 50 contacts of each 2.25 s duration, in the 2nd test series 50 contacts of 2.0 s duration per grinding process were made .

EXAMPLE 6

The commercially available alumina / zirconia eutectic abrasive grain was regarding grain size and

Crossed grain shape matched according to the procedure in the example 3 processed into grinding wheels, which were then tested according to the method of Example 2. The received Results are shown in Table 9.

Table 9

Abrasive grain

Commercial eutectic Al ₂ O ₃ / ZrO ₂ abrasive grain

Standard aluminum oxide abrasive grain G52E

Weight loss Metal removal from the disc (g) (g)

984

537

2.75

2.20

The commercial eutectic Al ₂ O ₃ / ZrO ₂ abrasive grain gave an 83% better grinding performance compared to the standard molten aluminum oxide.

EXAMPLE 7

The commercially available alumina / zirconia eutectic abrasive grain was cross-matched with regard to grain size and grain shape and then according to the procedure

130022/0712

of Example 4 for grinding wheels of type 27 with recessed Processed middle part, which were tested according to the method of Example 4. The specific weight of the eutectic abrasive grain was used in the batch composition and the compacting density of the discs are taken into account. The test results obtained with the discs are in Table 10 reproduced.

Table 10 Medium Grinding Quality Metal- behaves factor abrasive nis Abrasive grain Discs speed quality age (g / min) 21.14 595 Commercial eutek- 32.19 763 table Al ₂ O ₃ / ZrO ₂ - 28.15 Abrasive grain soft 23.70 13.64 341 hard 13.05 322 Standard aluminum 24.97 oxide abrasive grit EDR soft 24.66 hard

The grinding performance of the commercial aluminum oxide / zirconia eutectic abrasive grain was around 74-137% better than that of the molten abrasive grain Standard aluminum oxide.

The grinding performance of the commercially available alumina / zirconia abrasive grain according to the main claims and teachings of U.S. Patent 3,891,408 is better than that of normal fused alumina abrasive grain and similar, equal to and in some cases less than that of the abrasive grain according to the invention . Compared to the known eutectic Al ₂ O ₃ / ZrO ₂ abrasive grain, the abrasive grain according to the invention is distinguished by the fact that it surprisingly has a zirconium dioxide content

130022/0712

and a structure can be produced which is outside of the data given in US Pat. No. 3,891,408 _{for the Al 2} O _{3 / ZrO 2 system for optimum grinding performance at low and moderate pressure.} This equal or better grinding performance of the abrasive grain according to the invention is achieved by the presence of titanium dioxide or a reduced form thereof. By reducing the zirconium dioxide content in the abrasive grain while maintaining its excellent grinding performance, a significant reduction in manufacturing costs could be achieved.

130022/0712

Claims (17)

& FLORACK PATENT AGENCY OFFICE 30Λ0992 SCHUMANNSTH. Θ7. D-4000 DÜSSBLPORF Telephone: (0211) 683346 Telex: 08586513 cop d PATENT LAWYERS: Dipl.-Ing. W. COHAUSZ Dipl.-Ing. R. KNAUF Dr.-Ing., Dipl.-WirtJch.-lng. A. GERBER ■ Dipl.-Ing, H. B. COHAUSZ Claims 1/. Aluminum oxide abrasive grain, characterized in that that it is 27 to 35% by weight of zirconium dioxide, titanium dioxide or a reduced form thereof in an amount of 1 to 10% by weight as oxide, as well as impurities - if at all in a total amount of at most 3% by weight, expressed as oxides. 2. Abrasive grain according to claim 1, characterized in that it contains 1 to 5 wt .-% Contains titanium dioxide or a reduced form thereof, expressed as oxide. 3. Abrasive grain according to claim 1 or 2, characterized in that a reduced Form of titanium dioxide is present and is present as carbide, oxycarbide or suboxide of titanium. 4. Abrasive grain according to one of claims 1 to 3, characterized in that it contains at most 0.1 wt .-% Na ₂ O. 5. Abrasive grain according to one of claims 1 to 4, characterized in that it contains at most 1.5% by weight of SiO ₂ . 34 300
ü / un 130022/0712 6. Abrasive grain according to claim 5, characterized in that it contains less than 1 wt .-% SiO ₂ . 7. Abrasive grain according to claim 6, characterized in that it contains less than 0.5 wt .-% SiO ₂ . 8. Abrasive grain according to one of claims 1 to 7, characterized in that it contains a total of at most 1.5% by weight of MgO, CaO and Fe-O-. 9. Abrasive grain according to one of claims 1 to 8, characterized in that 10 up to 40% by weight of the zirconium dioxide is present in tetragonal crystal form. 10. Abrasive grain according to one of claims 1 to 9, characterized in that its Microstructure consists of primary aluminum oxide crystals that form a eutectic matrix of aluminum oxide and zirconia are embedded. ν 11. Abrasive grain according to claim 10, characterized ge indicates that the alumina primary crystals have a size of 5 to 50 µm and are predominantly smaller than 30 µm. 12. Method of making the abrasive grain according to a of claims 1 to 11, characterized in that a melt of the required Composed in less than 3 minutes by contacting with one heat-dissipating material is cooled. 130022/0712 13. The method according to claim 12, characterized that it cools down in less than 1 minute. 14. The method according to claim 13, characterized that it cools down in less than 20 seconds. 15. The method according to claim 12, characterized that as a heat-dissipating material metal balls, metal rods or metal plates or chunks of previously solidified abrasive grain can be used. 16. The method according to any one of claims 12 to 15, characterized in that the heat dissipating Material is introduced into the melt and taken out of it when a layer is formed solidified product has deposited on it. 17. Use of the abrasive grain according to one of the claims 1 through 11 for making a bonded abrasive. 130022/0712